Another method of measuring STM performance is the Brown-Peterson task
The subject is presented with a test item and is then immediately required to perform a distraction task which prevents rehearsal of the test item.
Brown and the Petersons study showed that in the absence of rehearsal forgetting took place very quickly.
STM storage requires rehearsal of some kind in order to keep the item in conscious attention.
When rehearsal is prevented items are lost from the STM very rapidly.